1. Field of the Invention
This invention relates generally to coffee roasters and other similar heating devices.
2. Prior Art
Coffee roasting is done by circulating a stream of hot air or process stream of several hundred degrees through coffee beans. The process stream is unavoidably contaminated by particulate matter, such as chaff or husks, and volatile organic compounds from the coffee. In industrial coffee roasting, pollution control guidelines set by the Environmental Protection Agency must be met for limiting the emission of smoke and odor. Specifically, exhaust air from a roaster must be heated to at least 1400 degrees Fahrenheit for at least 0.3 second to assure complete incineration of the volatile organic compounds and particulate matter. In addition to controlling emissions, the chaff must also be extracted from the coffee during roasting.
Various coffee roasters are within the prior art. U.S. Pat. Nos. 5,394,623 to Sewell; 5,372,833 to Farina; 5,230,281 to Wireman et al.; and 3,189,460 to Smith, Jr. each show a roaster with a burner for heating the process stream, and a cyclone separator for extracting chaff from the process stream. The burner is separate from the cyclone separator. U.S. Pat. No. 4,484,064 to Murray shows a coffee roaster with a blower circulating the process stream through a vented coffee container. U.S. Pat. No. 2,212,120 to Kneale et al. shows a roaster in which the process stream is circulated between a roasting chamber and a space with electric heaters. Some of these roasters require an incineration burner in addition to a heating burner that substantially increases energy consumption. Other roasters fully mix the combustion gases from the burner with the process stream. The combustion gases are cooled during the mixing process, and are discharged into the atmosphere at process stream temperature, which is too low to incinerate pollutants. Many of these roasters are once-through systems that draw in air from the outside, pass it through the heating process once, and discharge it. A typical once-through system consumes 100,000 btu/hr for heating the process flow with a heating burner, and an additional 700,000 btu/hr for incinerating pollutants with an incineration burner, so the total energy consumption is very high.
U.S. Pat. Nos. 5,709,542 to Rentzel et al. and 5,427,746 to Pereira et al. show pollution control devices. They each direct the process stream past a flame from a fixed burner into a flame tube where the process stream is thoroughly mixed with the combustion gases before exiting the same outlet. If the temperature inside the flame tube is high enough to incinerate pollutants, then the process stream would be heated to an unnecessarily high temperature, but if the temperature inside the flame tube is at process stream temperature, pollutants will not be incinerated. Therefore, these devices are not suitable for use in heating applications in which the process stream is recirculated.